live-preview: Add a button into the Component List to add a new component and to switch over to it

[hunger]

We need this functionality, but I do not want it in the upcoming release: It is pretty confusing that it switches to a different component -- which hides all the current work!

We need to have some information in the current component in preview on screen for that to be less surprising and offer a way to get back to the "main preview" somehow.